Pattern forming process and process for preparing semiconductor device utilizing said pattern forming process

A process for forming an etching pattern, comprising the steps of:

• selectively irradiating light to a clean surface of a material to be worked by etching, so as to form radicals from a photoradical forming substance in an atmosphere of the substance, the light having a wavelength not longer than the UV-ray absorption end of the photoradical forming substance;
• forming a modified portion having etching resistance at a photo-irradiated portion of the surface;
• and
• then subjecting an unmodified portion of the surface of the material to be worked to an etching treatment comprising dry etching using halogen atom radicals, thereby forming an etching pattern corresponding to a pattern formed by said light irradiation.